In recent years, the number of vehicles that have on-board navigation apparatus has been increasing rapidly. The on-board navigation apparatus maintains a digital map database and is capable of displaying traffic congestion and traffic accident positions on the map based on traffic congestion information and traffic accident information provided by a traffic information center as well as performing a route search using conditions including the aforementioned information.
In Japan, digital map databases are prepared by several companies. The problem is that map data contains errors due to the different base maps and digitizing technologies. The error depends on the digital map from each publisher.
In the traffic information, for example, in case latitude/longitude data of the position is presented alone in order to report for example a traffic accident position, on-board navigation apparatus may identify a different point on the road as a traffic accident position depending on the type of the digital database maintained by the apparatus.
In order to offset such incorrect transmission of information, in the related art, node numbers are defined for nodes such as intersections in a road network and link numbers are defined for links representing roads connecting nodes. A digital map database from each publisher stores intersections and roads in correspondence to node numbers and link numbers. For traffic information, a road number is identified by a link number and a point on the road is displayed in a representation that the road is XX meters away from the start of the link.
However, node numbers and link numbers defined on a road network must be changed to new numbers in case a road is constructed or modified. When a node number or link number is changed, the digital map database from each publisher must be updated. Thus, the method for transmitting position information on a digital map requires a huge cost of maintenance.
In order to solve such problems, the inventor of the invention proposed, in the Japanese Patent Application No. 214068/1999, a system where an information providing side transmits “road shape data” including a coordinate string showing the road shape in the road section of a predetermined length including the on-road position and “relative position data” showing the on-road position in the road section represented by the road shape data in order to report the on-road position, and a receiving side uses the road shape data to perform map matching, identifies the road section on a digital map, and uses the relative position data to identify the on-road position in the road section. The inventor proposed, in the Japanese Patent Application No. 242166/1999, a system where “supplementary information” is also transmitted including the road type, road number, number of crossing links in the road section, crossing link angles and intersection names, and a system where the transmission data amount of “road shape data” is reduced without causing erroneous matching at the receiving side.
In this case, map matching at the receiving side is made for example as follows:
As shown in FIG. 21, when the longitude/latitude data of the point P0(x0, y0) , P1(x1, y1), . . . , pk(xk, yk) is transmitted as (x0, y0) (x1, y1) , . . . , (xk, yk), the receiving side uses the map data read from its digital map database to select roads included in the error range about the point P0(x0, y0) as candidates, and narrows down the candidates by using the transmitted “supplementary information.” When a single candidate is finally selected, a position closest to the point P0(x0, y0) and the point Pk (xk, yk) on the road is obtained, and the section is assumed as a road section represented by the “road shape data.”
When the final candidate is not selected but the roads Q, R are selected as candidates, the points Q0, R0 on the candidate roads closest to the point P0(x0, y0) are obtained to calculate distance between P0 and Q0 and the distance between P0 and R0. This operation is repeated for each point P1 (x1, y1) , . . . , Pk (xk, yk) and a road section where the sum of the root mean square of the distances from each point P0, P1, . . . , Pk is smallest is obtained. This section is assumed as a road section represented by “road shape data” to identify the road section.
The traffic congestion section A-B is identified based on “relative data” transmitted from the start point of the road section obtained from “road shape data.”